Her early musical influences include Sarah Vaughan, Aretha Franklin, Ella Fitzgerald, Nina Simone, Dinah Washington, Peggy Lee, and Curtis Mayfield, among others.
McWilliams served as the primary female lead vocalist for the first two years of the band's existence, but voluntarily left the group in 1972, as she was exhausted from touring and wished to spend more time with her family.
[1] After leaving Rufus, McWilliams moved to Los Angeles, where she found steady work in advertising, singing jingles for over 600 radio and television spots.
Guitarist Phil Upchurch recommended her to producer Quincy Jones, who used her extensively on his Body Heat promotional tour, singing backing and lead vocals.
Over the same time period, she continued to work with Quincy Jones, appearing on the Michael Jackson album Off the Wall and its hit single "Don't Stop 'Til You Get Enough".
After working with Mathis, she auditioned for an open spot in Bette Midler's backing group the Harlettes, which she got, and ended up touring in support of her stage show The Divine Miss M, including an eight-week run on Broadway.
Since 2000, she has recorded and toured with Mary J. Blige, Celine Dion, Michael Buble, Jennifer Lopez, and Steely Dan, as part of their cadre of backing singers known as "The Danettes".